Identification of an equivalent viscous damping function depending on engineering demand parameters

This contribution provides an overview of the SINAPS@ French research project and its main achievements. SINAPS@ stands for “Earthquake and Nuclear Facility: Improving and Sustaining Safety”, and it has gathered the broad research community together to propose an innovative seismic safety analysis for nuclear facilities. This five-year project was funded by the French government after the 2011 Japanese Tohoku large earthquake and associated tsunami that caused a major accident at the Fukushima Daichi nuclear power plant. Soon after this disaster, the international community involved in nuclear safety questioned the current methodologies used to define and to account for seismic loadings for nuclear facilities during the design and periodic assessment review phases. Within this framework, worldwide nuclear authorities asked nuclear licensees to perform ‘stress tests’ to estimate the capacity of their existing facilities for sustaining extreme seismic motions. As an introduction, the French nuclear regulatory framework is presented here, to emphasize the key issues and the scientific challenges. An analysis of the current French practices and the need to better assess the seismic margin of nuclear facilities contributed to the shaping of the scientific roadmap of SINAPS@. SINAPS@ was aimed at conducting a continuous analysis of completeness and gaps in databases (for all data types, including geology, seismology, site characterization, materials), of reliability or deficiency of models available to describe physical phenomena (i.e., prediction of seismic motion, site effects, soil and structure interactions, linear and nonlinear wave propagation, material constitutive laws in the nonlinear domain for structural analysis), and of the relevance or weakness of methodologies used for seismic safety assessment. This critical analysis that confronts the methods (either deterministic or probabilistic) and the available data in terms of the international state of the art systematically addresses the uncertainty issues. We present the key results achieved in SINAPS@ at each step of the full seismic analysis, with a focus on uncertainty identification, quantification, and propagation. The main lessons learned from SINAPS@ are highlighted. SINAPS@ promotes an innovative integrated approach that is consistent with Guidelines #22, as recently published by the French Nuclear Safety Authority (Guidelines ASN #22 2017), and opens the perspectives to improve current French practice.

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Main Achievements of the Multidisciplinary SINAPS@ Research Project: Towards an Integrated Approach to Perform Seismic Safety Analysis of Nuclear Facilities

A discrete anisotropic damage constitutive law with an enhanced mixed-mode kinematics: Application to RC shear walls

Study on nonlinear damping behavior of damaged recycled aggregate concrete beams

Assessment of safety margins related to a seismic risk in Civil Engineering requires the improvement of the predictive methods usually performed. The damping phenomena still remain a major source of uncertainty both at the structure and the constitutive material levels. However, the resistance of the said structure to an earthquake is strongly conditioned by its ability to store and to dissipate the energy introduced by the ground motion. Better modeling and evaluation of these effects are therefore essential for the seismic risk assessment. This thesis takes place in the framework of the RSNR SINAPS@ project whose main objective is the improvement of modeling tools allowing to appreciate the effects of an earthquake from the rupture of the fault to the vibratory behavior of the structures and amenities.

Nonlinear local behaviours and numerical modeling of damping in civil engineering structures in dynamic

Dissipations in reinforced concrete components: Static and dynamic experimental identification strategy

Damage models, developed in the last decades, insure a continuous description of the fracture process zone in quasi-brittle materials but fail at representing fine information of the cracking features such as openings and spacings. Recently, the concept of displacement discontinuities embedded in to a standard finite element has been proved to be efficient in modeling fracture of quasi-brittle materials. The present paper aims at capturing crack openings in a natural way by using the Strong Discontinuity Approach (SDA). This later is coupled with a continuous anisotropic damage model accounting for different crack orientations and crack closure effects. A regularized version of the Dirac distribution and the hardening parameter provides+ the establishment of anenriched model compatible with the continuous one. Numerical simulations at the integration point level and a three-point bending test carried out on a single edge notched beam show the performances of the model.

Reduced kinematic formulation based on the strong discontinuity method for reinforced concrete components

When attempting to predict the seismic response of reinforced concrete (RC) structures, a trade-off has to be found between a realistic representation of the dissipations through material law and a numerically more efficient modelling with a controlled computational demand such as a Rayleigh-type damping model. Anyway, constitutive laws only describe internal dissipation and actually need a complementary dissipation term often chosen as a proportional damping matrix to take into account external dissipation sources such as interactions with the environment. Decoupling these two contributions in global dissipation measurement from experimental tests is still challenging. To address this problem, a numerical study based on an experimentally identified structural model is here presented. To this end, an experimental campaign has been carried out on RC beams set up on the AZALEE shaking table of the TAMARIS facility operated by the French Alternative Energies and Atomic Energy Commission (CEA). In this paper, the experimental campaign is briefly presented. Then, a parametric model is formulated and identified from the experimental results. Third, numerical dynamic experiments are carried out in order to assess the influence of several parameters on the energy dissipation and on the equivalent viscous damping ratio through two different methods. The validity of these results is assessed on a numerical case where a nonlinear model and an equivalent linear model are compared with each other. Experimental results of dynamic tests are also used as reference in order to estimate the additional viscous damping necessary to take into account the whole energy dissipation.

https://hal.archives-ouvertes.fr/hal-02418149/document

Damping capabilities of reinforced concrete components in the beyond design range from the identification to a critical review of common best-practices

B. Richard

Papers

Dissipations in reinforced concrete components: Static and dynamic experimental identification strategy

Reduced kinematic formulation based on the strong discontinuity method for reinforced concrete components

Damping capabilities of reinforced concrete components in the beyond design range from the identification to a critical review of common best-practices